The present invention relates to a drilling and/or chiseling tool according to the preamble to claim 1.
Tools are known from the prior art, for example from patent disclosures EP 0 761 927 A1, DE 100 38 039 A1, and DE 44 06 513 A1, which have a hard metal cutting element situated at the machining end of the tool head; a radially outer, second working region of the hard metal cutting element is set back in relation to a central, first working region of the hard metal cutting element and the two working regions transition into each other via a third working region. Trials with corresponding tools have shown that particularly when drilling concrete or plate-reinforced casings or steel casings, a borehole cross section is produced whose geometric form corresponds approximately to a so-called Reuleaux triangle. This borehole cross section is typical for drills with two cutting edges and it is produced because the outer ends of the cutting edges stick to the borehole wall or borehole rim. The point at which the cutting edge sticks temporarily becomes the rotation point for the entire tool, producing an outwardly curved lateral edge typical of the Reuleaux triangle. Tools with three main cutting edges produce borehole cross sections that are embodied in the form of squares with outwardly curved lateral edges. These out-of-round borehole cross sections result, for example, in difficulties when inserting metal dowel pins since these are designed for circular cross sections and cylindrical boreholes. The circle inside the Reuleaux triangle is too small for the dowel pin.